Aspects of the present disclosure relate generally to a dynamic caterpuller system for applying loads to a buffer tube of a fiber optic cable during manufacturing of the same.
Buffer tubes may be manufactured by extrusion processes. The fiber optic elements (e.g., glass optical fibers with glass core(s) in polymer-coated glass cladding) are typically protected by a polymer tube that is extruded around the elements. Typically up to twelve fibers may be inserted into a single buffer tube, which may have dimensions of about 2.5 millimeters (mm) in diameter. Normally buffer tubes are stranded around a central element, such as a rod of glass reinforced plastic (GRP). This resulting assembly is then covered with a polymer sheath or jacket (e.g., polyethylene jacket) to protect the cable against environmental elements.
To improve mechanical performance of the resulting cable, excess fiber length (EFL) has to be very carefully controlled, where the EFL is the relative length difference between the length of the fiber optic elements and the buffer tube. A typical value of the EFL is on the order of about 0.05% of stranded tubes and up to about 0.5% for central-tube cable designs, where the buffer tube is put in the center of the cable and strength elements may be arranged around the buffer tube. In either case, control of the EFL during manufacturing may be important to the stress and strain performance of the resulting cable.
State-of-the-art buffer tube manufacturing equipment 10 typically includes the following components (see FIG. 1): a fiber pay-off 12, an extruder 14, a clinching caterpuller 16 (also called “caterpillar”), a wheel capstan 18, and a tube take-up 20. The fiber optic elements, covered with a high-viscous gel are inserted into the extruder 14, where the gel applicator may be located before the extruder 14 in a manufacturing line. The polymeric tube is then extruded around the fibers. After the extruder, the buffer tube is typically cooled down in a water trough, passed through the clinching caterpuller 16, and guided around a wheel capstan 18. The buffer tube is guided between belts of the clinching caterpuller 16, which are moderately pressed to the buffer tube to reduce slippage therebetween.
By adjusting the speed difference between the wheel capstan 18 and the clinching caterpuller 16, the tube is tensioned or compressed longitudinally. As a result, EFL can be adjusted in a wide range. This manufacturing process relies upon a close contact between the surface of the buffer tube and belts of the caterpuller 16. As a result the buffer tubes may get deformed when the forces of the belts are too high and when the tube is still too soft (molten; not completely cooled down following extrusion). Such an effect becomes even more salient when the tube diameter is below 2.5 mm. Aspects of the present disclosure seek to overcome such problems.